The major objectives of this research project are to determine the mechanisms responsible for volume regulation in dog regulation in dog erythrocytes. When dog erythrocytes are exposed to anastomotic media, the is an activation of either the Na/H antiporter or K-C1 cotransport systems to return the cell back to its normal volume. Studies in our laboratory have been designed to quantitate these pathways and determine the stoichimetry, inhibitors and activators of these transport systems. Recent studies have been design to determine the heterogeneity of cells have been assayed for their ion and water content as well as their specific density. Future studies will be designed to determine the transport properties of these cell fractions in order to explain the physiological mechanism responsible for these observations. It is anticipated that the results of these studies will allow us to determine the mechanisms responsible for cell volume regulation in vivo.